Background Art With reference to a rolling process that produces steel strips with a predetermined thickness, variation in the thickness of the strips is a serious problem, which is caused by roll eccentricity. In particular, in case of hot rolling thin steel materials, for example, D&I (Drawing & Ironing) slabs, periodic variation in thickness due to the roll eccentricity adversely affects the qualities of finished products.

In order to assist understanding of the present invention, a hot rolling process will be described briefly. Slabs from a continuous cast process are charged in a heating furnace and uniformly heated to an appropriate temperature.

Then, the slabs extracted from the heating furnace are rolled in a roughing mill to produce sheet bars with a thickness of 60 mm or less. The sheet bars so obtained are rolled in a finishing mill to produce steel strips, which are heat treated and finally coiled. The steel strips must satisfy the required conditions for final hot rolled products for buildings and automobiles and the gauge required for subsequent process (cold rolling process).

Recently, the thickness and width qualities of hot rolled products are required to be high-graded in order to decrease a unit cost. In particular, the

thickness of the hot rolled products is required to be accurate and constant within a predetermined range.

The aforementioned finishing mill comprises multiple (typically seven) roll stands. Sheet bars are rolled into steel strips with a desirable gauge including thickness in the finishing mill in such a manner that a rolling condition such as pressure, speed and position is determined depending on thickness and type of the sheet bars, and temperature, using a finishing mill setting model; the determined rolling condition is initially set up ; and the sheet bars are rolled while dynamically controlling the rolling condition using information obtained during rolling to produce the steel strips with desirable gauge.

As described above, although rolled products are required to have accurate and constant thickness, thickness variation is caused by various factors.

Roll eccentricity in a rolling mill is a major contributor to such thickness variation.

Conventionally, in addition to manual manipulation by an operator, the following methods have been used to monitor roll eccentricity: First, a roll force method which keeps the roll force constant can be used to remove effects of the eccentricity on thickness at the outlet. Unfortunately, this method has a problem in that a roll gap is inappropriately controlled owing to other disturbance factors (variations in thickness and hardness of steel materials to be rolled, and the like) affecting the roll force. In order to solve this problem, generally, an additional device for correction of thickness is required.

Second, the Smith method based on the principle of a gauge meter may be used. However, a major disadvantage of the Smith method arises from use of a rectifying device, whereby noise signals are remarkably detected from controlled signals and amplitudes. Second large signal (second harmonic) among roll eccentricity signals is mainly caused by ovality of a work roll. That is, because the diameter of the work roll does not correspond to 1/2 the diameter of a backup roll, removal efficiency of the second harmonic from the control signal is decreased.

Third, a method disclosed in U. S. Patent Nos. 3,920, 968,4, 763,273 and the like, so-called Fourier analysis (hereinafter, simply referred to as'FARE') may be used. According to the FARE, a roll eccentricity value is calculated to control a roll gap. An input signal for the FARE is equal to the combined signals from a load cell and a pulse generator, which are coupled to the end of a backup roll. As

an eccentricity signal obtained by the FARE passes through a pressure control loop, the roll gap is controlled to increase or decrease a roll force for correcting the eccentricity. A signal corresponding to the roll force for correcting the eccentricity is continuously accumulated until a roll eccentricity component disappears from a roll force signal. An output from the FARE is not stored in a memory until the eccentricity component is detected. However, the FARE method is complex in terms of an operation step and a constitution. Furthermore, a large number of items must be calculated and a result analysis cannot be easily carried out. In particular, in order for an operator to understand an analysis result, an additional procedure for transformation of the analysis result to the time domain is required.

One example for detecting roll eccentricity in the time domain is disclosed in Korean Patent Application No. 2000-80034 filed by the present applicant, titled "method for detecting eccentricity in rolling mill using non-linear curve fitting".

According to this method, respective eccentricities of upper and lower backup rolls are isolated and detected from a beat waveform generated by the diameter difference between the upper and lower rolls, instead of using a sensor such as a pulse generator. In this case, there is an advantage in that each eccentricity magnitude can be accurately obtained. However, in case of applying the sum of respective eccentricities to actual eccentricity control, larger eccentricity may be caused. Therefore, actual eccentricity control is difficult.

Disclosure of the Invention Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for detecting a fundamental wave and harmonics of roll eccentricity caused by a lack of concentricity between the rotation center and the geometric center of the roll using the pulse signal from a pulse generator and the roll force signal from a load cell.

It is another object of the present invention to provide an apparatus for detecting roll eccentricity, which gives excellent detection efficiency even under severe working conditions.

In accordance with one aspect of the present invention, the above and

other objects can be accomplished by the provision of a method for detecting roll eccentricity in a rolling mill, comprising the steps of a) inputting data with respect to a roll force of the mill, a pulse signal from a pulse generator, an input and an output signal of a steel material to be rolled; b) determining whether the input signal of the material and a marker pulse signal from the pulse generator are inputted; c) storing the roll forces corresponding to respective sample pulse signals from the pulse generator in buffers; d) calculating respective roll force variations by subtracting an average roll force from respective roll forces stored in the buffers; e) detecting the fundamental wave and harmonics of the eccentricity by non-linear curve fitting signals corresponding to the roll force variations; and f) determining whether the output signal of the material is inputted, wherein when the output signal is inputted, the detection process is terminated but otherwise, the steps of c)-f) are iterated.

In accordance with another aspect of the present invention, there is provided an apparatus for detecting roll eccentricity in a rolling mill, comprising a cover surrounding the shaft of the roll in the rolling mill ; a pulse generator with multiple proximity sensors, which is installed in a proper position on the cover; and a clamp wheel with multiple blades, which rotates around a concentric axis of the roll and the clamp wheel in a state that is coupled with the roll shaft, wherein whenever the roll completes a rotation, the sensors detect the multiple blades, and generate one marker pulse and multiple sample pulses from each sector with a constant rotation angle, which are synchronized with roll force signals.

Hereinafter, the method and apparatus for detecting eccentricity in a rolling mill using a pulse generator will be described in more detail with reference to the preferred embodiments illustrated in the accompanying drawings.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a flow chart showing a method for detecting roll eccentricity in a rolling mill using a pulse generator according to the preferred embodiment of the present invention;

Fig. 2a is a graph showing a detection result for roll eccentricity in a rolling mill according to the method shown in Fig. 1; Fig. 2b is a graph showing a roll force signal after contr ling roll eccentricity according to the method of the present invention ; Fig. 2c is a graph showing a frequency analysis result according to the present invention ; Fig. 3 is an assembled perspective view showing an apparatus for detecting roll eccentricity according to the preferred embodiment of the present invention; Fig. 4 is a perspective view showing a housing for a pulse generator in the apparatus of Fig. 3; Fig. 5 is a perspective view showing a roll cover in the apparatus of Fig.

3; Fig. 6 is a front view showing a clamp wheel coupled with the roll shaft, wherein the clamp wheel is positioned in the roll cover; Fig. 7 is a perspective view of the apparatus of Fig. 3 in a state wherein the roll cover and the housing are separated from each other; Fig. 8 is a perspective view of the housing of Fig. 4 in a state wherein an upper housing and a lower housing are separated from each other; Fig. 9 is a perspective view of the lower housing in a state wherein proximity sensors are installed therein; Fig. 10 is a cross sectional view of the apparatus of Fig. 3 in a state wherein the pulse generator is coupled with the roll cover; Fig. 11 is an enlarged view of"A"part in Fig. 10; Fig. 12 is a constitutional block diagram showing a signal processing unit which is installed in the pulse generator; and Fig. 13 is a view showing a pulse waveform from the pulse generator in the apparatus of the present invention, and a four-multiplied pulse waveform thereof.

Best Mode for Carrying Out the Invention Roll eccentricity in a rolling mill equals to the composite waveform or the sum of a fundamental, second harmonic, third harmonic,... and nth harmonic which

are generated whenever a backup roll completes a rotation, and is expressed as a roll force signal. The waveform has a strong relationship with generation factors thereof. Generally, the roll eccentricity is expressed by equation 1 below: Equation 1 <BR> <BR> <BR> <BR> <BR> <BR> <BR> co<BR> <BR> n-. i wherein, the first right side represents a fundamental wave of the eccentricity and the second right side represents a second harmonic of the eccentricity, el, e2,..., and en represent respective signal magnitudes corresponding to roll force variations due to the fundamental wave and the harmonics of the eccentricity. 1, $ 2,..., and $, represent respective phases of the fundamental wave and the harmonics of the eccentricity. By appropriately determining such parameters, components of the roll eccentricity can be detected from the roll force signal.

According to the present invention, the above parameters are estimated using a non-linear curve fitting method. The vector of the parameters can be expressed as equation 2: Equation 2 Xopi=minsum(F0(X0t)-F0(t))2 wherein, X represents the vector of the parameters (el, e2,..., en, 1, 2, ..., c"), F (X, t) represents a calculated roll force with time at the set vector value, Fa (t) represents a signal corresponding to variation in a detected roll force.

Therefore, the objective of the equation 2 is to find the vector X allowing the calculated roll force to approximate to the detected roll force.

According to the present invention, a rolling process is carried out as shown in Fig. 1. That is, Fig. 1 is a flow chart showing a method for detecting roll eccentricity in a rolling mill using a pulse generator according to one preferred embodiment of the present invention.

In Fig. 1, first, rolling data with respect to roll force signals from respective load cells of rolling mill stands, pulse signals from a pulse generator, an input and

output signals of a steel material to be rolled are inputted into a computer (step Sol).

The reason why the pulse generator to be described hereinafter is used is to input a roll force signal per constant rotation angle of a backup roll into a computer.

Conventionally, whenever the backup roll completes a rotation, the pulse generator generates one marker pulse at a specific position and a number of sample pulses at respective sectors with a constant rotation angle. The pulse generator used herein generates 1 marker pulse and 64 sample pulses per one rotation of a roll, for example, a backup roll. Therefore, according to the preferred embodiment of the present invention, whenever the backup roll rotates at an angle of 360/64, corresponding roll force signals are inputted. That is, a total of 64 roll force signals per one rotation of the backup roll are inputted.

In step S1, if the rolling data are collected, whether the input signal of the steel material and the marker pulse signal are inputted is determined (step S2). If both the signals are inputted (yes), roll forces are synchronized with the sample pulse signals and stored in buffers (step S3). In this case, the sample pulse denotes a pulse generated at each sector with an equally divided rotation angle for each rotation of a backup roll whose circumference is equally divided into n sectors.

The marker pulse denotes a pulse providing a standard point to the position of the backup roll and generates one pulse per one rotation of the backup roll.

According to the present invention, respective roll force signals at the sectors are stored until the backup roll rotates m times. That is, as described in the above, if 64 roll force signals per one rotation of the backup roll are inputted, total 64 x m roll force signals are used to detect the roll eccentricity. Because the rotation number m of the backup roll affects the curve fitting result, it is preferable to select a value m such that if the value n is small, the value m is large, and vice versa.

If respective roll forces are stored until the backup roll rotates m times in step S3, an average roll force is calculated. Then, the average roll force is subtracted from respective roll forces to thereby produce respective roll force variations, which are in turn stored in buffers (step S4). Then, initial values of the parameters in the equation 1 are appropriately selected using signals corresponding to the stored roll force variations, followed by the non-linear curve fitting using the equation 2 (step S5).

Optimum parameters are obtained using the non-linear curve fitting of step

S5. Then, the fundamental wave and its harmonic (second harmonic) components (magnitude and phase) of the eccentricity are detected using the optimum parameters (steps S6, S7). In this case, the fundamental wave and second harmonic denote roll force variations caused by the roll eccentricity.

When the above step S7 is completed, whether the output signal of the steel material is inputted (whether a rolled steel material exits the rolling mill) is determined (step S8). When the material exits the rolling mill (yes), the detection process is terminated; otherwise (no), the above steps of S3-S7 are iterated.

Meanwhile, where the backup roll rotates m+1 times during rolling, first n number data when the backup roll rotates once are excluded from the data stored in buffers and the non-linear curve fitting to the remaining data is constructed. As a result, the fundamental wave and second harmonic of the eccentricity are detected.

Although the detection process of the fundamental wave and second harmonic of the roll eccentricity is described on the basis of the backup roll, the same process can also be applied to a work roll. Furthermore, the above process can be applied to the backup roll and work roll at the same time to detect the eccentricity in a rolling mill. In addition, it is possible to detect the fundamental wave and harmonics (including second harmonic, third harmonic and the like) of the roll eccentricity in a rolling mill.

Fig. 2a is a graph showing roll eccentricity detected according to the method of the present invention. That is, Fig. 2a shows roll force variation components caused by the roll eccentricity, which are extracted from signals corresponding to roll force variations during rolling. In Fig. 2a, a fundamental wave and a second harmonic are shown respectively. Abscissa represents the number of pulse generated according to the rotation of the backup roll. 64 pulses are generated whenever the backup roll completes a rotation. As shown in Fig. 2a, whenever the backup roll completes a rotation, the fundamental wave generates 64 pulses per a period, while the second harmonic generates 32 pulses per a period.

The roll force signal equals to the sum of the fundamental wave and the second harmonic. As shown in Fig. 2a, the roll force signal, fundamental wave and second harmonic respectively take the form of a sine curve and have almost the same phase. Therefore, it can be seen that the detection result according to the method of the present invention is excellent.

Fig. 2b is a graph showing a roll force signal after controlling roll

eccentricity according to the method of the present invention. It can be seen from Fig. 2b that the eccentricity control starts from 650 pulses and the roll force is largely decreased after 650 lses. A dotted line represents a gap compensation signal for removing the roll eccentricity. Fig. 2c shows a frequency analysis result.

The solid line represents the frequency analysis result before controlling the roll eccentricity and the dotted line represents the frequency analysis result after controlling the roll eccentricity.

Meanwhile, Figs. 3 to 12 show an apparatus for detecting roll eccentricity in a rolling mill according to the method as described in the above. The apparatus comprises a circular clamp wheel to be rotated with a backup roll in a state that is coupled with the shaft of the roll, and in which multiple blades are fixedly installed with equal circumferential spacing; multiple proximity sensors which are separated from the blades of the clamp wheel by a predetermined distance ; and a signal processing unit for generating pulses of integer multiple of the blades by processing signals detected by the multiple proximity sensors.

According to the preferred embodiment of the present invention, three proximity sensors are used. A first and a second proximity sensors detect multiple blades which are positioned with equal circumferential spacing at the one edge of the clamp wheel, thereby generating the sample pulses as described in the above.

A third proximity sensor detects one blade which is positioned at the other edge of the clamp wheel, thereby generating one marker pulse per one rotation of the roll.

Hereinafter, the apparatus for detecting roll eccentricity in a rolling mill according to the present invention will be described in more detail with reference to the accompanying drawings.

First, with reference to a roll cover 2 which is coupled with a pulse generator, as shown in Figs. 3 and 5, the roll cover 2 surrounds the shaft of a roll 5 (see Fig. 10) which is coupled with a clamp wheel 20 (see Fig. 6), on one edge of which multiple (16 as shown in the drawings) blades 22 for sample pulse generation are positioned with equal circumferential spacing and on the other edge of which one blade 22'for mark pulse generation is positioned. The roll cover prevents lubricant sprayed at the shaft of the roll 5 from splashing outward. In addition, the roll cover is installed on one side of a housing 1 of the rolling mill as shown in the drawings in order to guarantee safe operation by an operator, and support the sensors installed for sensing the blades on the clamp wheel 20. As shown in Fig. 3, the roll

cover 2 is coupled with the pulse generator 100 for detecting roll eccentricity on a proper circumferential position of the cylindrical body thereof, one end of which is clogged. The roll cover 2 is formed on the clogged end with a watching window 7, through which the inner state of the roll cover is viewed. A through-hole 3 is formed at the circumferential position of the roll cover 2, on which the pulse generator 100 is installed in a coupling manner. A vertical frame 8'is installed around the through-hole. The upper end of the vertical frame is coupled with a support member 8 (see Figs. 5 and 7). The support member 8 is fastened to the pulse generator 100 with a bolt. Preferably, the upper surface of the support member 8 is formed with a long groove 9 along the inner edge thereof. An O-ring is slid into the groove 9 in order to prevent fluid leakage or air stream through a gap defined between the support member 8 and the pulse generator 100.

As shown in Figs. 6,7 and 10, the clamp wheel 20 has the appearance of a circular ring. The clamp wheel is constituted of two separable semi-circular elements 21a, 21b, which enclose the end portion (actually, the shaft) of the roll 5.

Opposite ends of the two semi-circular elements 21a, 21b are hingedly coupled with each other. The other ends are coupled with each other by a buckle 25. In this regard, the clamp wheel 20 is fixedly coupled with the shaft of the roll or is separated from the shaft of the roll. That is, the clamp wheel 20 is fixedly coupled with the shaft of the roll 5 in such a manner that the shaft of the roll 5 is positioned in the two semi-circular elements 21 a, 21b of the clamp wheel 20 and then the semi- circular elements are buckled together. The clamp wheel 20 is formed with blades 22 for generation of multiple, preferably 16 sample pulses on the one edge thereof with equal circumferential spacing. The other edge of the clamp wheel is formed with one blade 22'for generation of a marker pulse.

Meanwhile, a pulse generator 100 detects the blades 22, 22' on the clamp wheel 20 to be rotated with the roll during rolling and generates an appropriate pulse signal. Preferably, the pulse generator comprises three proximity sensors 41,42, 43; a housing 10 for supporting the three proximity sensors 41,42, 43 as shown in the drawings; a signal processing unit 70 which is installed at a proper position in the housing 10; and a cable 99 for transmitting data to an external computer in a state that is connected with the signal processing unit 70.

As shown in Figs. 4, and 7 to 10, the housing 10 of the pulse generator is comprised of an upper housing 1 OH and a lower housing 1 OL. The housing 10 of

the pulse generator 100 is installed on the roll cover 2 in such a manner that the flanges of the upper and lower housing 10H, 10L are contacted with each other; the bolt holes of the lower housing 1 OL are coincided with those of the support member 8 and the housing i fastened to the support member with bolts. The housing 10 so installed receives the three proximity sensors 41,42, 43 and the signal processing unit 70 as shown in the drawings. The signal processing unit 70 comprises a signal transducer 71, an amplifier 72, a four x multiplier 73 and an RS-485 transducer 74, as shown in Fig. 12. As far as the housing 10 is concerned, the upper housing 1 OH is coupled with a cable connecting member 80. The lower surface of the lower housing 1 OL has a curved surface with the same curvature as that of the clamp wheel 20, which is fixedly coupled with the shaft of the roll 5.

The lower surface of the lower housing 10L is formed with three holes 12, through which the three proximity sensors 41,42, 43 are inserted. The proximity sensors 41, 42,43 have screw portions, respectively. Therefore, the sensors are installed in the housing 10 in such a manner that the sensors are inserted in the respective holes 12, and respective upper and lower parts thereof are fastened to the housing with nuts 45. If the nuts 45 are loosened, the sensors 41,42, 43 can move in upper and lower direction from the lower surface of the lower housing 10L.

Therefore, the sensors can be separated from the clamp wheel 20 by an appropriate distance. It is preferable to limit the distance to a range of about 10 to 20 mm. If the holes 12 on the lower housing 10L are large, the respective sensors can also move in left and right direction.

As shown in Figs. 7 and 10, the lower surface of the lower housing 10L is provided with a sensor protector 30. The sensor protector 30 is formed with three through-holes 31,32, 33. The proximity sensors 41,42, 43 are protruded from the lower surface of the lower housing lOL and are positioned in the through-holes 31, 32,33 of the sensor protector 30, respectively. The through-holes 31,32, 33 of the sensor protector 30 have a diameter of about 15 mm larger than the proximity sensors 41, 42,43. This is to ensure that the sensor protector 30 does not interfere with the left and right movement of the sensors 41,42, 43 within the holes 12. The center portion of the sensor protector 30 is formed with a through-hole 37. When a bolt 47 that is inserted in a through-hole on the center of the lower housing 10L passes the through-hole 37, the bolt 47 is fastened with a nut 46. In this manner, the sensor protector 30 can be fixedly installed at the lower housing 1 OL.

Meanwhile, one side of the upper housing 1 OH of the pulse generator 100 is provided with a cable connecting member 80, as shown in Figs. 10 and 11. The cable connecting member 80 is provided with a connecting tube having a screw portion on the rear end thereof. The connecting tube is coupled with a jig 96 which is positioned at the front end of a cable 99. Therefore, the cable 99 can be connected to the pulse generator 100. According to the preferred embodiment of the present invention, the rear end of the jig 96 is coupled with a quick coupling 97, which is in turn fixedly connected to an outer casing 98 for cable protection. The front end of the cable 99 which is positioned in the outer casing 98 is provided with a connector 95, which is in turn connected with another connector 75 which is positioned in the cable connecting member 80.

A signal processing unit 70 is built in the one side of the housing 10 of the pulse generator 100. The signal processing unit 70 comprises a signal transducer 71, an amplifier 72, a four x multiplier 73 and an RS-485 transducer 74, as shown in Fig. 12. The proximity sensors 41,42, 43 detect sensing signals. The detected signals are inputted in the signal transducer 71 and transformed. The transformed signals are amplified in the amplifier 72. Pulses from the sensors 41,42 are four- multiplied in the four x multiplier 73. The four-multiplied pulse signals are outputted to an external computer (not shown) through the transducer 74 and the cable 99.

Fig. 13 shows pulse waveforms output from the proximity sensors. A first proximity sensor 41 detects a front blade among 16 blades on the clamp wheel 20 and generates a pulse 41P. On the other hand, a second proximity sensor 42 detects a rear blade that is positioned behind the front blade and generates a pulse 42P.

As used herein, the term"front blade"denotes a specific blade on the basis of the rotation direction of the clamp wheel 20 according to driving of the roll 5, and the term"rear blade"denotes a subsequent blade. The front and the rear blades vary depending on whether the roll 5 rotates in a clockwise or a counterclockwise direction. The reason why the front and the rear blades are defined is to define blades to be detected by the first proximity sensor 41 and the second proximity sensor 42.

A third proximity sensor 43 detects the number of rotations of the clamp wheel 20. That is, the third proximity sensor 43 detects one blade 22'that is

formed on one edge of the clamp wheel 20 whenever the wheel 20 completes a rotation. The other edge of the clamp wheel 20 is formed with total 16 blades 22, as shown in the drawings. Where these blades are detected, sample pulses are generated. Where the generated sample pulses are four-multiplied, a total of 64 pulses 48P are obtained whenever the clamp wheel 20 completes a rotation.

As described in the above, for each rotation of the roll, a total of 16 sample pulses is generated by the first and the second proximity sensors 41,42, which are separated from the clamp wheel 20 of the roll 5 by about 10 to 12 mm. The third proximity sensor 43 generates one marker pulse.

The pulses 41P, 42P generated from the first and the second sensors 41,42 have pulse waveforms with a 90° phase angle as shown in the upper and the medium parts of Fig. 13. Because 16 pulses are generated for each rotation of the roll 5, if the pulses are four-multiplied in the four x multiplier 73, a total of 64 pulses 48P are generated by one rotation of the roll 5.

The apparatus of the present invention has very efficient construction and durability. Therefore, roll eccentricity can be detected even in severe working conditions in an accurate and reliable manner.

Industrial Applicability As apparent from the above description, the present invention provides a method and an apparatus for detecting roll eccentricity in a rolling mill using a pulse generator, in which the fundamental wave and harmonics of the roll eccentricity can be detected using the pulse signal from the pulse generator and the roll force signal from a load cell. Such detection can be carried out even in severe working conditions, in which high temperature and pressure lubricant is present, in a reliable manner.

In addition, if the fundamental and harmonic components of the roll eccentricity detected according to the present method are provided to an operator through on-line, the operator can change rolls at appropriate times based on such information. At the same time, because the roll eccentricity can be controlled in real time, thickness variation in rolled products can be decreased.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.